Multi-phase converters are widely used as power supplies for electronic devices. In computer systems, to provide regulated voltage for microprocessors, interleaved multi-phase topologies operating with 2 to 64 phases are often employed. They can provide regulated voltages ranging from 0.9V to 5V and supply a large amount of currents, which in some applications reaches 150 A. In modern TV sets and consumer electronics multiple converters are used to provide different supply voltages for various system blocks. Multi-phase converters operating in parallel can also be found in systems, whose power consumption increases in time. Examples include computer servers and large communication systems, where new system blocks (units) can be added to increase systems power delivery capabilities.
Traditionally, the controllers for these power supplies are implemented using application specific analog circuits. They usually require a large number of external passive elements for implementation and have proven to be prone to stability problems when operating with parallel converters. In addition, they are often designed to control a very specific power stage only.
As a valuable alternative digital controllers could be applied. In multi-stage converters advantages of digital controllers over traditional analog solutions are becoming more evident. Potentially, they can result in system realization with a smaller number of components, allow simpler introduction of novel power management and control techniques, such as dynamic and adaptive voltage scaling (AVS and DVS), and are easier for integration with other system parts that are predominantly digital.
The digital implementation of multi-phase pulse width modulators can bring advantages such as accurate matching of multiple pulse-width modulated signals and/or reduction of the output voltage ripple through phase shifting. However, compared to analog solutions most of the multi-phase digital pulse-width modulation (MDPM) architectures suffer from the problem of relatively high power consumption (from several tens to hundreds of milliwatts) that is linearly increasing with switching frequency. The high power is likely to hinder the use of most of the existing digital solutions in upcoming low-power converters, which are expected to operate at switching frequencies 10 to 100 times higher than the existing power stages. As a result, a significant reduction in converter efficiency can be expected. In addition, the utilization of flexibility of digital control has been limited to abovementioned applications. Even though digital control allows implementation of flexible architectures, application specific digital architectures that can be used only for specific types of multi-phase converters are usually used. Besides that, the IC realization of some of the proposed solutions is costly since they require a relatively large chip area.
Digital control of low-power switch-mode power supplies (SMPS) can result in significant improvements of the characteristics of power supply system used in applications such as communication systems, consumer electronics, portable devices, and computers. The advantages of digital control include flexibility, low sensitivity on external influences and realization with a small number of external passive components.
Digital implementation also simplifies implementation of power supplies. Analog controllers usually require time-consuming redesign every time characteristics of the supplied devices change, which in modern electronics happens often. On the other hand, modern tools for automatic digital design allow short development process and fast modification of existing designs to accommodate new requirements.
Although the advantages of the digital realizations are known, in low-power applications, analog pulse width modulator (PWM) controllers are mainly used.
One of the main reasons for the sporadic use of digital controllers is lack of low-power hardware solutions for digital-pulse width modulators (DPWM), the key parts of every voltage-mode pulse-width modulation controller. The DPWMs operate at high switching frequencies, which in existing switching converters exceed 1 MHz, and need to have high resolution. The high resolution is necessary for tight output voltage regulation and for elimination of undesirable limit-cycle oscillations of the output voltage and inductor current.
In existing DPWM solutions the power consumption is usually proportional to the product of switching frequency and resolution and, in some cases, exceeds the power consumed by the output load, resulting in poor overall efficiency of digitally controlled SMPS.